This invention relates generally to a starting apparatus for cranking an internal combustion engine, and more specifically relates to a pinion gear assembly for momentarily engaging an engine flywheel and transferring power from a starter motor to the internal combustion engine.
The concept and various embodiments of automatically engaging and disengaging starting mechanisms for internal combustion engines are well-known. Such pinion gears may be engaged mechanically, or by their own inertia, and the assembly may be allowed to slip, or twist or to compress, to properly align the teeth of the pinion gear with the teeth of the flywheel or ring gear. The disclosed embodiment of the invention is a pinion gear assembly of the inertia type, which compresses for alignment, although, as will become apparent, the novel construction of this pinion gear assembly allows its use with the mechanically-engaged and the tension of controlled-slip type of pinion gear assemblies. A conventional mechanism comprises a plurality of teeth in the flywheel in an internal combustion engine or in a ring gear secured to the crank shaft of such an engine, adjacent a pinion gear coupled to the output shaft of a starting motor. In the mechanically-engaged pinion gear, when the starter motor is actuated and begins to rotate, a separate solenoid, operating a lever arm, forces the pinion gear towards the flywheel or ring gear, and into engagement with its teeth. When the starter motor is deactivated, a spring forces the pinion gear assembly out of engagement with the teeth of the ring or flywheel gear, and back along motor shaft. With the inertia type of pinion gear assembly, when the starting motor is actuated and begins to rotate, the inertia of the pinion resists rotation, and a helical spline on the motor shaft causes the pinion to translate actually along the motor shaft and into engagement with the gear teeth associated with the engine crank shaft. The engine is thus cranked until the engine speed passes through the speed at which the starting motor drives it, momentarily releasing the load from the teeth of the pinion gear and allowing a spring biasing force to disengage the pinion gear from the engine gear.
As will be apparent, when the pinion gear approaches the flywheel or ring gear, the teeth of the two gears are randomly oriented, and the pinion gear may strike against the sides of the teeth of the pinion or ring gear rather than engage these teeth. The starter motor will continue to rotate, and some means must be provided to absorb the shock of impact between the gears, allow relative movement of the gears until they engage, or allow axial movement of part of the pinion gear assembly without actual movement of the pinion gear under the influence of a rotating, helical splined shaft. Typically, a resilient or friction material is interposed between a spline follower and the pinion gear, to allow twisting or slipping rotation of the spline follower with respect to the pinion gear, or to allow axial movement between the spline follower and pinion gear, or both. The disclosed embodiment of the invention uses a resilient member, allowing axial movement only, although the concepts disclosed are equally applicable to a pinion gear assembly utilizing twisting or controlled slip.
Numerous modifications and improvements have been made to this basic mechanism. However, numerous deficiencies and problems still remain. Among such difficulties is the difficulty of maintaining proper alignment between a pinion gear and the spline follower portion of a pinion gear assembly, particularly in pinion gear assemblies used on smaller engines. As will be apparent, the pinion gear and spline follower portions of a pinion gear assembly move on a common shaft, and misalignment between these two portions causes rapid wear of the pinion gear assembly, or of the shaft, and often results in failure to crank, or failure to disengage the pinion gear assembly binding on the starting motor shaft. This may also result in starting motor failure from overspeeding.
Attempts have been made to provide a structure for a pinion gear assembly which is not subject to misalignment upon assembly. Such structures have generally required extensive and precise machining operations, or a welded or brazed assembly.
A particular difficulty of modifying this mechanism is the dimensional constraint placed upon its size by associated components. Commonly, the starter mechanism will be positioned within a housing or adjacent engine components which closely limit its size. Therefore, unless redesign of the entire starting motor assembly and perhaps even engine components is permitted, refinements to the starter mechanism must be made within dimensional limits established by these associated components. The development of a new component or production technique thus leaves to the additional consideration of adapting such an improvement to the presently utilized components.
A conventional starter motor pinion gear assembly includes an outer metal cup or shell which secures, in operating relationship, a spline follower, a resilient washer member which may function as a friction clutch, and the pinion gear itself. The cup is secured to the pinion gear, and these components are moved as previously explained, with the spline follower following splines in the starter motor shaft. Prior art pinion gears are commonly hobbed or drop-forged and may easily be attached to the drawn cup by conventional means such as welding or brazing, as is taught by U.S. Pat. No. 3,071,013. The recently developed capability of forming the pinion gears of powdered metal and then sintering them produces an improved pinion gear, but does not solve the difficulties with regard to the assembling of pinion gear assemblies. Conventional welding and brazing techniques, while ultimately capable of performing such a bonding operation, reliably do so only under carefully controlled conditions, and the rejection rate of completed assemblies and the difficulties inherent in such a bonding process offset the advantages of a powdered metal pinion gear.
Also, while welding and brazing techniques may be used at assembly to provide a pinion gear assembly with adequate alignment between its members, this advantage is offset by the high rate of rejection of completed welded or brazed assemblies. A starter drive pinion gear assembly which uses a powdered metal pinion gear and which can be assembled without welding or brazing is shown in applicant's prior application, Ser. No. 965,158, filed Nov. 30, 1978, now U.S. Pat. No. 4,255,982 date Mar. 17, 1981, and entitled "Starter Assembly Utilizing a Castellated Cup". This pinion gear assembly is of the twist or controlled-slip type, and includes a pinion gear having an annular base, the cup having an open end in a castellated configuration, the protrusions of the castellation being folded down between the teeth of the pinion gear, against the annular base. In production, this technique may not always provide acceptable alignment, due to nonuniformity of the metal of the cup, so that when applying uniform force to each of the castellation portions, the castellated portions may move unequally, some not contacting the annular base, and some forcing the pinion gear into the resilient washer, misaligning the pinion gear. Also, this type of construction is limited to those applications where there is physically room for a cup member with large enough castellations to be practically bent into position with a reasonable degree of repeatability.
It has also been proposed to place such a powdered metal pinion gear through a correspondingly-serrated opening in the bottom of a cup member, placing a resilient washer and spline follower into the cup, and then folding previously-slotted tabs formed in the edge of the open end of the cup against the back of the spline follower, retaining the spline follower in the cup and preloading the rubber washer. While usable with smaller engines and more constrained spaces, this approach is subject to severe misalignment, the tabs, typically four in number, not folding inward and downward evenly under identical pressure due to nonuniformity of material about the periphery of the cup member. Such a cup member may be made by stamping or drawing.
Pinion gear assemblies which overcome such deficiencies have been constructed but have been unable to utilize the advantage of powdered metal pinion gears, and have required extensive machining. One such device known to applicant is machined on all surfaces, and has a pinion gear member integral with the cup member. There is a cup member, a short axial protrusion from one end of the cup member, and a pinion gear on this protrusion. Such a shape must necessarily be a machined cast shape, with the outside of the cup machined by turning, the short axial protrusion being machined by turning, and the pinion gear portion at the end of the axial protrusion being then machined by hobbing or broaching. This inside of the cup portion must be machined, as must the bore through the axial protrusion and pinion gear. Further, a snap ring groove is machined near the opened end of the cup member for receiving a snap ring which holds a resilient washer and cam follower in the cup member. The cup member is also provided with four indentations around its perimeter, aligned with matching recesses in the periphery of the spline follower, thus locking the spline follower to the cup member for use as a inertia drive starter coupling of the compression type.
As will be apparent, such a construction is not only unnecessarily costly and subject to numerous assembly operations, leading to numerous individual sources of error and a high rate of rejection of such assemblies.